Effects of Rates and Split Applications of Nitrogen Fertilizer on Soil and Leaf Nutrients Levels, Quality and Harvesting Age of Ratoon Crop of Two Sugarcane Varieties in Western Kenya

Abstract

Sugarcane is the third most important commodity crop in Kenya after tea and coffee. Though high yielding and early maturing varieties have been introduced in Kenya Sugar Industry to overcome low yields, the problem persists. Farmers apply nitrogen either in single dose or split. It is not known if the rates and mode of application are appropriate for the new varieties. The industry pays farmers based on tonnage of delivered millable cane, but is considering changing payment to a combination of yield and quality. It is not known if the payment method shall be influenced by agronomic inputs and timing of harvesting period. The objective of this study was to establish the influence of nitrogen fertilizer applied either in single or split to ratoon crop of new (D8484) and old (C042 I) varieties on soil and leaf nutrients levels, cane yields, quality and optimal harvesting age. The experimental design was a 2x4x3 split split-plot on a continuation of a research at Kenya Sugar Research Foundation, Opapo, where the plant crop received similar treatments. Analysis of soil and leaf nutrients levels, cane yields and quality parameters was done using recommended methods. The results showed that at start and at harvest of ratoon crop, the soil pH remained within the range suitable for sugarcane growing. There were no significant treatment effects on soil P, Ca, Mn, Zn and Fe levels. Only soil K significantly (p:SO.OS)declined due to variety D8484 at O-IScm at harvest and at both start ofratooning and harvest at IS-30cm soil depth. Significant (p:SO.OS)leaf %N values were recorded due to varieties from the Sthto io" MAR. Leaf nitrogen contents in both varieties were similar in the 3rd and 4th MAR, peaked at Sth MAR and decreased thereafter. Throughout the monitoring period, variety D8484 out-yielded (p:SO.OS)C042I. Pol%, brix% and sugar yields were significantly influenced by varieties and N rates. Based on commercial sugar yield, it is concluded that, ratoon crops of varities C042I and D8484can be harvested at 18thand 1i h MAR, respectively. Leaf sampling and nutrients analysis should be done before Sth MAR. Nitrogen rate of 60 kgN/ha may be adopted in order to realize profitable sugar yield while split application may be done for other reasons like ensuring uniformity in application and spreading cash flow, but not for yields and commercial sugar benefit